FIG. 1 is a top schematic diagram showing the bonding structure between two circuit substrates according to a prior art. When two circuit substrates 10, 50 are bonded, two circuits on the two circuit substrates 10, 50 are electrically connected to each other via contact pads 11 and 21 at the bonded interface between these two circuit substrates 10 and 50. Especially, in assembling the display panel, such as the liquid crystal display (LCD), the organic electro-luminescence display (OELD) and the plasma display panel (PDP), the surface mount technique (SMT), tape automated bonding (TAB), chip on glass (COG) and chip on film (COF), the aforementioned technique are generally employed.
FIG. 2 illustrates the conduction principle of the circuits on circuit substrates 10 and 50. The circuit on the circuit substrate 10 is covered by an insulating layer 41 and the end of the circuit is exposed to form the contact pad 11. The contact pad 21 on the circuit substrate 50 is electrically connected to the circuit of the circuit substrate 10 via an anisotropic conductive film (ACF) 30. The anisotropic conductive film 30 includes an insulator 31 and a plurality of conductive particles 32 distributed in the insulator 31, and the conductive particles 32 are disposed of an insulating film on their surfaces. The anisotropic conductive film 30 is disposed between two contact pads 11, 21 and thermally compressed as the circuit substrates 10 and 50 are bonded. The insulating film is destroyed to conduct two circuits of these two circuit substrates via the contact pads 11, 21.
In the prior art of TAB and COF, the material of the circuit substrate, which carries the integrated circuit (IC), is transparent, it assures the reliability of the circuit connection to observe whether the contact pads are matched and the conductive particles between the contact pads are deformed or not. But this technique cannot be applied to an opaque circuit substrate.
In a prior art, as shown in FIG. 3 and FIG. 4, a contact pad 130 on a circuit substrate has a chink 131 at the center. In assembling the two circuit substrates, the chink 131 is covered by the contact pad 210 as shown in FIG. 3 if the contact pads 130, 210 are matched well, which indicates an validated circuit connection; and the chink 131 is pervious to light as shown in FIG. 4 if the contact pads 130, 210 are mismatched, which indicates a bad circuit connection. This prior art does not provide an instant method of inspecting the reliability of the circuit connection.
FIG. 5 is a schematic diagram showing another prior art, the dummy pads 140 and a window 141 are formed on two bonded circuit substrates respectively. The condition of matching the window 141 and the dummy pads 140 indicates the reliability of circuit connection of two bonded circuit substrates. But, this technique does not provide the instant inspection.
FIG. 6 is a schematic diagram showing the prior art, there are contact pads 210, 150 on two circuit substrates, wherein the contact pad 150 has sidewalls on its both edges to form the bonding pads 151. When the contact pads 210, 150 are thermally compressed, the amount of the conductive particles 32, constrained between the bonding pads 151, of the anisotropic conductive film is enough to avoid the conductive particles 32 spilling to damage the conduction. Again, this prior art does not provide the instant inspection.
The quality of contact-pad connection affects the reliability of the circuit connection of two bonded circuit substrates, and the main two factors are whether the contact pads are matched or not and contact quality of the anisotropic conductive film. The post-fabricated inspection is a big drawback in assembling two circuit boards. More especially, in assembling the LCD, it costs and spends much to measure white/black dots on the screen of the LCD for inspecting the reliability of the circuit connection after the LCD is assembled. An instant method of inspecting circuit connection in bonding two circuit substrates is essential for providing developers information and condition to modify the environmental parameters to enhance the reliability of the circuit connection.